Sequence studies of the human genome demonstrate that almost half of the DNA is derived from mobile elements. Most of the current retrotransposition activity arises from L1 and the L1-dependent, non-autonomous elements, such as Alu, contributing to a significant amount of genetic mutation and genomic instability. We present data demonstrating that nickel chloride, but not cobalt chloride, is able to stimulate L1 retrotransposition about 2.5-fold. Our data suggest that the stimulation occurs at a post-transcriptional level, possibly during the integration process. The effect of nickel on the cell is highly complex, limiting the determination of the exact mechanism of this stimulation. The observed stimulation of L1 retrotransposition is not due to a general increase in L1 transcription or an increase in the number of genomic nicks caused by nickel, but more likely caused by a decrease in DNA repair activities that influence the downstream events of retrotransposition. Our observations demonstrate the influence of environmental toxicants on human retroelement activity. We present an additional mechanism for heavy-metal carcinogenesis, where DNA damage through mobile element activation must be considered when dealing with genomic damage/instability in response to environmental agents.

Nuclear hormone receptors, such as the estrogen receptors (ERs), are regulated by specific kinase signaling pathways. Here, we demonstrate that the p38 MAPK stimulates both ERalpha- and ERbeta-mediated transcription in MCF-7 breast carcinoma, Ishikawa endometrial adenocarcinoma, and human embryonic kidney 293 cells. Inhibition of this potentiation using the p38 inhibitor, RWJ67657, blocked estrogen-mediated transcription and proliferation. Activated ERs promote gene expression in part through the recruitment of the p160 class of coactivators. Because no direct p38 phosphorylation sites have been determined on either ERalpha or beta, we hypothesized that p38 could target the p160 class of coactivators. We show for the first time using pharmacological and molecular techniques that the p160 coactivator glucocorticoid receptor-interacting protein 1 (GRIP1) is phosphorylated and potentiated by the p38 MAPK signaling cascade in vitro and in vivo. S736 was identified as a necessary site for p38 induction of GRIP1 transcriptional activation. The C terminus of GRIP1 was also demonstrated to contain a p38-responsive region. Taken together, these results indicate that p38 stimulates ER-mediated transcription by targeting the GRIP1 coactivator.

Therapy employing the fluoroquinolone antibiotic, trovafloxacin (TVX) was curtailed due to idiosyncratic hepatotoxicity. Previous studies in mice showed that a nonhepatotoxic inflammatory stress induced by tumor necrosis factor alpha (TNF) synergized with a nonhepatotoxic dose of TVX to cause liver injury. The purpose of this study was to explore mechanisms by which TVX interacts with TNF to cause liver injury. TVX pretreatment prolonged the peak of plasma TNF after its administration. This prolongation of TNF by TVX was critical to the development of hepatotoxicity. The prolongation of TNF concentration in plasma was primarily due to reduced clearance when compared with secondary biosynthesis. TNF is cleared from plasma by binding to soluble TNF receptors (TNFRs) which are eliminated by the kidney; however, the plasma concentrations of soluble TNFRs were not reduced, and biomarkers of renal dysfunction were not elevated in TVX/TNF-treated mice. Two injections of TNF mimicked the prolongation of the TNF peak by TVX and caused liver injury, but injury was less severe than after TVX/TNF coexposure. TVX enhanced the induction of proinflammatory cytokines by TNF. Additionally, TVX sensitized Hepa1c1c7 cells to TNF-induced killing in a concentration-dependent manner and increased both potency and efficacy of TNF to activate effector caspases that were critically involved in cell death from TVX/TNF coexposure. In summary, TVX reduced the clearance of TNF independent of either receptor shedding or kidney dysfunction. Additionally, TVX interacted with TNF to enhance inflammation and sensitize hepatocytes to TNF-induced cell death.

Halothane (2-bromo-2-chloro-1,1,1-trifluoro-ethane) is an inhaled anesthetic that induces severe, idiosyncratic liver injury, i.e., "halothane hepatitis," in approximately 1 in 20,000 human patients. We used known human risk factors (female sex, adult age, and genetics) as well as probable risk factors (fasting and inflammatory stress) to develop a murine model with characteristics of human halothane hepatitis. Female and male BALB/cJ mice treated with halothane developed dose-dependent liver injury within 24 h; however, the liver injury was severe only in females. Livers had extensive centrilobular necrosis, inflammatory cell infiltrate, and steatosis. Fasting rendered mice more sensitive to halothane hepatotoxicity, and 8-weekold female mice were more sensitive than males of the same age or than younger (4-week-old) females. C57BL/6 mice were insensitive to halothane, suggesting a strong genetic predisposition. In halothane-treated females, plasma concentration of tumor necrosis factor-␣ was greater than in males, and neutrophils were recruited to liver more rapidly and to a greater extent. Anti-CD18 serum attenuated halothane-induced liver injury in female mice, suggesting that neutrophil migration, activation, or both are required for injury. Coexposure of halothane-treated male mice to lipopolysaccharide to induce modest inflammatory stress converted their mild hepatotoxic response to a pronounced, female-like response. This is the first animal model of an idiosyncratic adverse drug reaction that is based on human risk factors and produces reproducible, severe hepatitis from halothane exposure with lesions characteristic of human halothane hepatitis. Moreover, these results suggest that a more robust innate immune response underlies the predisposition of female mice to halothane hepatitis.

Severe halothane (HAL)-induced hepatotoxicity occurs in one in 6000-30,000 patients by an unknown mechanism. Female sex is a risk factor in humans and rodents. We tested the hypothesis that a sex difference in natural killer (NK) cell activity contributes to HAL-induced liver injury. HAL (15 mmol/kg, ip) treatment resulted in severe liver injury by 12 h in female, wild-type BALB/cJ mice, and the magnitude of liver injury varied with stage of the estrous cycle. Ovariectomized (OVX) mice developed only mild liver injury. Plasma interferon-gamma (IFN-γ) was elevated 10-fold in HAL-treated females compared with similarly treated male mice or with OVX female mice. IFN-γ knockout mice were resistant to severe HAL-induced liver injury. The deactivation of NK cells with anti-asialo GM1 treatment attenuated liver injury and the increase in plasma IFN-γ compared with immunoglobulin G-treated control mice. Mice with a mutated form of perforin, a protein involved in granule-mediated cytotoxicity, were protected from severe liver injury. Furthermore, HAL increased the activity of NK cells in vivo, as indicated by increased surface expression of CD69, an early activation marker. In response to HAL, NK cell receptor ligands on the surface of hepatocytes were expressed in a manner that can activate NK cells. These results confirm the sexual dimorphic hepatotoxic response to HAL in mice and suggest that IFN-γ and NK cells have essential roles in the development of severe HAL-induced hepatotoxicity.